This invention relates to a control apparatus of a hybrid vehicle, and particularly to a control apparatus that sets both upper and lower limit-determining voltages according to a main battery open-circuit voltage, which can increase battery life by preventing an over-charge and an over-electric discharge of a main battery, and can improve reliability of the whole system because the life of the battery is increased.
Some motor vehicles are of a type commonly called a hybrid vehicle having an internal combustion engine and an electric motor disposed therein as the power sources of a propulsion system. The hybrid vehicle further includes an engine control means for controlling a running state of the engine and motor control means for controlling an operating state of the motor. The engine control means and the motor control means detect respective operating states of the engine and the motor when the vehicle is traveling, and then exchange such detected data regarding the running states. As a result, the respective operating states of the engine and the motor are controlled in association with one another. Such a control system attains a high level of required performance (such as fuel efficiency, lower values of detrimental components in exhaust gases, and improves power performance).
One such example of a control apparatus of a hybrid vehicle is disclosed in published Japanese Application Laid-Open No. 11-332017. The control apparatus for a hybrid vehicle in this disclosure includes an engine which has a vehicle-propelling source, a power-generating electric motor providing both operations for generating an assisting output which assists engine output from a power supply energy of a battery apparatus having an accumulation of stored electricity and as a power-generating motor for generating energy to charge the battery apparatus. A power-generating motor control means executes an operation control of the power-generating motor. The power-generating motor control means controls the operation of the power-generating motor so as to keep electric power of the motor generated to the battery apparatus below a predetermined maximum limit value according to a quantity of accumulation of electricity in the battery apparatus. The motor control means prevents an excessive reduction of voltage between terminals in electric discharging and an excessive rise of voltage between terminals in charging of the battery apparatus which gives electricity to and receives electricity from the power-generating motor.
A control apparatus of a traditional hybrid vehicle has a lot of control elements (i.e. driving output, internal resistance, battery temperature, electric discharge depth) involved with the main battery voltage during motor driving, which are reflected in motor control. It is thought that the control values (limit values) change in discontinuity greatly, and there is an inconvenience or problem in that the control does not always converge (instability).
This invention solves the above-mentioned problem, and provides a control apparatus that can limit the usable range of a main battery by limiting motor driving depending on a state of the main battery. The control apparatus, in order to improve battery life and reliability, does not let a battery discharge electricity to less than a predetermined voltage (avoiding over-electric discharge), and executes main battery voltage charging below a predetermined voltage (preventing over-charge).
In order to obviate or minimize the above problem or inconvenience, the present invention provides a control apparatus for a hybrid vehicle having an engine and a motor disposed therein as a vehicle-propelling system, the motor being connected to an output shaft and having both driving and power-generating functions. The control apparatus includes an engine control means which controls a running state of the engine and a motor control means which controls both driving and power-generating states of the motor independent from the control of the engine by the engine control means. The motor control means has a function to detect an open-circuit voltage of a main battery when motor driving is stopped, to set an upper limit-determining voltage and a lower limit-determining voltage of the main battery for motor driving according to the main battery open-circuit voltage.
According to the present invention as previously described, at motor driving stop or off, a motor control means detects the open-circuit voltage of the main battery, and both upper and lower limit-determining voltage values for motor driving are set for the main battery according to the main battery open-circuit voltage. As a result, the system can prevent an over-charge and an over-electric discharge of the main battery, and it is possible to extend battery life.